Impactos del pastoreo del ciervo de los cayos, una especie en peligro de extinción, sobre el también amenazado pinar rupícola: ¿un dilema conservativo?

In the lower Florida Keys, endangered Key deer (Odocoileus virginianus clavium) herbivory, along with fire, can affect pine rocklands, an endangered plant community. We compared pineland vegetation from three studies over approximately 50 years on four islands with either high or low deer density (historical analysis). We also compared extant vegetation samples between two islands with high or low deer density, which contained pinelands burned 10 years and 14 years prior to sampling and control areas (unburned for > 50 yr). In addition, experimental deer exclosures and control plots established in pineland were prescribe burned and analyzed for deer effects on an island with high density of Key deer. The historical analysis suggests that, over time, deer–preferred plant species declined while less–preferred species increased, regardless of fire history on islands. The extant vegetation analysis suggests that fire and Key deer herbivory both reduce hardwood plant density and growth. Densities of deer–preferred woody species were higher on an island with low deer density than on an island with high deer density in burn treatments, but relatively similar in control areas. On the high deer density island, a fire effect was evident in that the control area had higher densities of woody species than burned areas, and herbaceous species richness was higher in the control area, indicating a possible refuge from deer herbivory. In deer exclosures, preferred woody species and herbaceous species tended to increase after fire, but decrease in adjacent open plots. Results suggest that Key deer herbivory, along with fire, shapes pine rockland plant communities, and that overbrowsing might have substantial impacts on preferred herbaceous and woody species in pinelands. Therefore, efforts could be confounded in managing both the endangered Key deer and the endangered pine rocklands that they affect.En los cayos del sur de Florida, el pastoreo del ciervo de los cayos (Odocoileus virginianus clavium), junto con los incendios, pueden afectar a los pinares rupícolas, una comunidad vegetal en peligro. Hemos comparado la vegetación de los pinares de tres estudios llevados a cabo durante aproximadamente 50 años en cuatro islas con densidades de ciervos altas o bajas (análisis histórico). También comparamos muestras de vegetación existentes en dos islas con una densidad alta y baja de ciervos, que contenían pinares quemados 10 y 14 años antes del muestreo con áreas de control (sin incendiar durante más de 50 años). Además, se incendiaron intencionadamente y se analizaron parcelas experimentales con exclusión de ciervos y de control, para conocer los efectos de los ciervos en una isla con una gran densidad de éstos de los cayos. El análisis histórico sugirió que, con los años, las especies de plantas preferidas por los ciervos decayeron, mientras que las menos preferidas proliferaron, independientemente de los incendios sufridos. El análisis de la vegetación existente sugiere que tanto los incendios como la alimentación de los ciervos reducen la densidad y el crecimiento de la vegetación leñosa. Las densidades de las especies leñosas preferidas por los ciervos eran mayores en la isla con una densidad baja de ciervos, que en la isla con una densidad alta de ciervos tras los incendios, pero eran relativamente similares en las áreas de control. En la isla con una mayor densidad de ciervos, los efectos del fuego eran evidentes, ya que el área de control poseía mayores densidades de especies leñosas que las áreas incendiadas, y la riqueza de especies herbáceas era mayor en la zona de control, lo que indicaba que se trataba posiblemente de un refugio ante los ciervos. En las zonas cerradas a los ciervos, las especies herbáceas y las leñosas preferidas por los ciervos tendían a aumentar tras el incendio, pero disminuían en las áreas abiertas adyacentes. Los resultados sugieren que el pastoreo del ciervo de los cayos, junto con el fuego, dan forma a las comunidades vegetales rupícolas, y que el sobrepastoreo puede tener un impacto sustancial sobre las especies herbáceas leñosas preferidas de los pinares. Por lo tanto, los esfuerzos para la gestión, tanto del amenazado ciervo de los cayos como de los pinares rupícolas afectados por éste, también en peligro, podrían ser contradictorios

Direct and Legacy Effects of Long-Term Elevated CO2 on Fine Root Growth and Plant-Insect Interactions

Increasing atmospheric CO2 concentrations alter leaf physiology, with effects that cascade to communities and ecosystems. Yet, responses over cycles of disturbance and recovery are not well known, because most experiments span limited ecological time. We examined the effects of CO2 on root growth, herbivory and arthropod biodiversity in a woodland from 1996 to 2006, and the legacy of CO2 enrichment on these processes during the year after the CO2 treatment ceased. We used minirhizotrons to study root growth, leaf censuses to study herbivory and pitfall traps to determine the effects of elevated CO2 on arthropod biodiversity. Elevated CO2 increased fine root biomass, but decreased foliar nitrogen and herbivory on all plant species. Insect biodiversity was unchanged in elevated CO2. Legacy effects of elevated CO2 disappeared quickly as fine root growth, foliar nitrogen and herbivory levels recovered in the next growing season following the cessation of elevated CO2. Although the effects of elevated CO2 cascade through plants to herbivores, they do not reach other trophic levels, and biodiversity remains unchanged. The legacy of 10yr of elevated CO2 on plant-herbivore interactions in this system appear to be minimal, indicating that the effects of elevated CO2 may not accumulate over cycles of disturbance and recovery

Seasonal variation in the relative dominance of herbivore guilds in an African savanna

African savannas are highly seasonal with a diverse array of both mammalian and invertebrate herbivores, yet herbivory studies have focused almost exclusively on mammals. We conducted a 2-yr exclosure experiment in South Africa's Kruger National Park to measure the relative impact of these two groups of herbivores on grass removal at both highly productive patches (termite mounds) and in the less productive savanna matrix. Invertebrate and mammalian herbivory was greater on termite mounds, but the relative importance of each group changed over time. Mammalian offtake was higher than invertebrates in the dry season, but can be eclipsed by invertebrates during the wet season when this group is more active. Our results demonstrate that invertebrates play a substantial role in savanna herbivory and should not be disregarded in attempts to understand the impacts of herbivory on ecosystems

Elevated CO2 Influences Nematode-Induced Defense Responses of Tomato Genotypes Differing in the JA Pathway

Rising atmospheric CO2 concentrations can affect the induced defense of plants against chewing herbivores but little is known about whether elevated CO2 can change the induced defense of plants against parasitic nematodes. This study examined the interactions between the root-knot nematode Meloidogyne incognita and three isogenic tomato (Lycopersicon esculentum) genotypes grown under ambient (390 ppm) and elevated (750 ppm) CO2 in growth chambers. In a previous study with open-top chambers in the field, we reported that elevated CO2 increased the number of nematode-induced root galls in a JA-defense-dominated genotype but not in a wild-type or JA-defense-recessive genotype. In the current study, we tested the hypothesis that elevated CO2 will favor the salicylic acid (SA)-pathway defense but repress the jasmonic acid (JA)-pathway defense of plants against plant-parasitic nematodes. Our data showed that elevated CO2 reduced the JA-pathway defense against M. incognita in the wild-type and in a genotype in which defense is dominated by the JA pathway (a JA-defense-dominated genotype) but up-regulated the SA-pathway defense in the wild type and in a JA-defense-recessive genotype (jasmonate-deficient mutant). Our results suggest that, in terms of defense genes, secondary metabolites, and volatile organic compounds, induced defense of nematode-infected plants could be affected by elevated CO2, and that CO2-induced changes of plant resistance may lead to genotype-specific responses of plants to nematodes under elevated CO2. The changes in resistance against nematodes, however, were small relative to those reported for chewing insects

Beyond climate envelopes: effects of weather on regional population trends in butterflies

Although the effects of climate change on biodiversity are increasingly evident by the shifts in species ranges across taxonomical groups, the underlying mechanisms affecting individual species are still poorly understood. The power of climate envelopes to predict future ranges has been seriously questioned in recent studies. Amongst others, an improved understanding of the effects of current weather on population trends is required. We analysed the relation between butterfly abundance and the weather experienced during the life cycle for successive years using data collected within the framework of the Dutch Butterfly Monitoring Scheme for 40 species over a 15-year period and corresponding climate data. Both average and extreme temperature and precipitation events were identified, and multiple regression was applied to explain annual changes in population indices. Significant weather effects were obtained for 39 species, with the most frequent effects associated with temperature. However, positive density-dependence suggested climatic independent trends in at least 12 species. Validation of the short-term predictions revealed a good potential for climate-based predictions of population trends in 20 species. Nevertheless, data from the warm and dry year of 2003 indicate that negative effects of climatic extremes are generally underestimated for habitat specialists in drought-susceptible habitats, whereas generalists remain unaffected. Further climatic warming is expected to influence the trends of 13 species, leading to an improvement for nine species, but a continued decline in the majority of species. Expectations from climate envelope models overestimate the positive effects of climate change in northwestern Europe. Our results underline the challenge to include population trends in predicting range shifts in response to climate change

The Effect of Plant Inbreeding and Stoichiometry on Interactions with Herbivores in Nature: Echinacea angustifolia and Its Specialist Aphid

Fragmentation of once widespread communities may alter interspecific interactions by changing genetic composition of interacting populations as well as their abundances and spatial distributions. In a long-term study of a fragmented population of Echinacea angustifolia, a perennial plant native to the North American prairie, we investigated influences on its interaction with a specialist aphid and tending ants. We grew plant progeny of sib-matings (I), and of random pairings within (W) and between (B) seven remnants in a common field within 8 km of the source remnants. During the fifth growing season, we determined each plant's burden of aphids and ants, as well as its size and foliar elemental composition (C, N, P). We also assayed composition (C, N) of aphids and ants. Early in the season, progeny from genotypic classes B and I were twice as likely to harbor aphids, and in greater abundance, than genotypic class W; aphid loads were inversely related to foliar concentration of P and positively related to leaf N and plant size. At the end of the season, aphid loads were indistinguishable among genotypic classes. Ant abundance tracked aphid abundance throughout the season but showed no direct relationship with plant traits. Through its potential to alter the genotypic composition of remnant populations of Echinacea, fragmentation can increase Echinacea's susceptibility to herbivory by its specialist aphid and, in turn, perturb the abundance and distribution of aphids

Successional Change in Phosphorus Stoichiometry Explains the Inverse Relationship between Herbivory and Lupin Density on Mount St. Helens

The average nitrogen-to-phosphorus ratio (N?P) of insect herbivores is less than that of leaves, suggesting that P may mediate plant-insect interactions more often than appreciated. We investigated whether succession-related heterogeneity in N and P stoichiometry influences herbivore performance on N-fixing lupin (Lupinus lepidus) colonizing primary successional volcanic surfaces, where the abundances of several specialist lepidopteran herbivores are inversely related to lupin density and are known to alter lupin colonization dynamics. We examined larval performance in response to leaf nutritional characteristics using gelechiid and pyralid leaf-tiers, and a noctuid leaf-cutter.Apple JL, Wink M, Wills SE, Bishop JG (2009) Successional Change in Phosphorus Stoichiometry Explains the Inverse Relationship between Herbivory and Lupin Density on Mount St. Helens. PLoS ONE 4(11): e7807. doi:10.1371/journal.pone.000780